Synchronizing system



Jan. 26, 1937. w. G. H. FlNCH SYNCHRONIZING SYSTEM 2 Sheets-Sheet 1' Original Filed Feb. 26, 1936 I I/I,"

5 W I I I I I 3 Jan. 26, 1937. w. G. H. FlNCH 2,069,061

SYNCHRONI ZING SYSTEM Original Filed Feb. 26, 1956 2 Sheets-Sheet 2 Auo/O AMPLIFIER unwary. 3119 27243 1 BY MW ATTORNEY.

Patented Jan. 26, 1937 UNITED STATES PATENT OFFICE Original application February 26, 1936, Serial No. 65,869. Patent No. 2,047,863, dated July 14, 1936. Divided and this application April 15.

1936, Serial No. 74,419

6 Claim.

This invention relates to synchronizing systems and circuits therefor for maintaining electromechanical systems in phase synchronization particularly applicable to telepicture systerns and is a division of application Ber. N0.

4 65,869, filed February 26, 1936, now Patent No.

2,047,863, granted July 14, 1936.

In accordance with my present invention the synchronizing signal is transmitted during a prell) determined portion of the rotation cycle, for example, during the underlap period of a picture drum transmitter. The synchronizing signal is intermittently impressed upon an intermediate stage of the picture signal amplifier during the no picture intervals. The receiver is maintained in at least approximate synchronization by a well known synchronous motor or synchronous drive means, and the synchronizing signal is operative during the receiver drum underlap period to maintain the drum in phase synchronism with the transmitter drum in a manner to be described in detail.

. It is accordingly an object of my present invention to provide novel apparatus for and means a of synchronizing electromechanical apparatus at remote points.

It is another object of my invention to provide novel circuits for efficient synchronous control of a telepicture system.

a It is a further object of my invention to pr vide novel apparatus and circuits for maintaining a telepicture receiver in phase ,synchronism with a corresponding transmitter.

These and further objects of my invention will become apparent from the following description taken in connection with the drawings, in which:

Figure 1 is a schematic representation of a preferred telepicture transmitter, and

Figure 2 isa corresponding diagrammatic representation of a telepicture receiver employing my novel phase synchronizing system.

Referring to Figure 1, a source of light generates a beam i focused to a point by a, lens system 2 upon the picture to be transmitted which is mounted on the cylindrical drum 3. If the picture is scanned one hundred lines per inch, the diameter of the light spot focused upon the picture should be .01 inch. The refracted. beam 4 from the picture is focused upon the photoelectric cell 5 by lens system 2'. The intensity of the refracted beam 4 is proportional to the shading of the picture elements which are successively moved past the light beam I. The picture drum 3 is rotated by shaft 6 driven by synchronous motor 1. Motor is preferably connected to a commercial electrical supply system 8, for example, a 60 cycle, 110 volt system. Reduction gearing, not shown, reduces the motor I speed to, for example, 100 revolutions per minute at shaft 6.

The anode potential for the photoelectric cell ii is supplied by the potentiometer 9 connected across a suitable direct current voltage source it. Condenser ll by-passes the potentiometer 8 section to ground. The cathode i2 of the 10 photoelectric cell 5 is connected to the control grid i3 of a screen grid modulator tube It by means of connection lead It. The control grid i2 is adiustably biased by means of potentiometer I! connected across a suitable grid biasing source ii. The grid bias for control grid I3 is supplied from the potentiometer it through the grid input resistance It.

Screen grid i9 is connected to a suitable potential point on the direct current source 20 through an impedance choke 2|. The anode 22 is connected to the potential source 20 through an impedance choke 22. A tone generator 50, schematically indicated, produces an altemating current potential across two potentiometers 25 24 and 26. The tone generator 50 may be an audio frequency vacuum tube oscillator, or an alternating current generator driven by an electric motor or preferably geared to motor I. The alternating current signal from tone generator 3 50 is coupled to the screen grid l9 through a coupling condenser 26. The impedance choke 2| prevents the tone signal from being by-passed to groundthrough the potential source 20.

The varying light beam 4 produces corresponding electrical variations at the control grid i3 of vacuum tube I4 as is well known inthe art. Introducing a tone or carrier signal from generator to the screen grid l9 corresponds to the well known'screen grid modulation method. The 4 signal produced in the output circuit of the vacuum tube ll across the impedance choke 23 is coupled to the control grid 21 of amplifier stage r 29 by means of the coupling condenser 29. A milliammeter 30 inserted in series with the anode 45 22 circuit in lead 23 serves as a visual indication of the operating condition of the telepicture transmitter.

When no light impinges upon the photo-cell .5, the control grid l3 has a potential corresponding to the adjusted bias by potentiometer i6 and the tone or carrier signal output of the vacuum tube ll will be at a minimum. The indication of the milliammeter 30 will accordingly also be at a minimum. When a bright spot is u scanned on the picture being transmitted, the potential of control grid is will correspondingly increase. The anode 22 current will therefore also increase. The indication of milliammeter 36 will correspondingly increase. The alternating current or carrier current output proportionately increases as is well known to those skilled in the art. Meter 3G accordingly indicates the functioning of the telepicture transmitter.

The control grid 2i of amplifier tube 28 is im pressed with an alternating current signal of frequency equal to the generated tone E6 and amplitude modulated in accordance with the yarying intensity of the light beam d impinging. on the photo cell b. The grid bias for control grid 2? is supplied by the bias battery 3i connected to the grid 2? through grid resistor 32. The primary of audio transformer 33 is connected in the output circuit of amplifier stage 28. The secondary of transformer 33 is connected to the input audio amplifier it, for further amplification of the telepicture signals for transmission to a remote station. The output tl-t? of audio ampliher 69 may be connected to a land transmission line, or to a radio transmitter for modulating a radio frequency carrier wave'for radiation to a remote receiver as is well known in the art.

Synchronization of the transmitter and receiver picture drums is accomplished by means of a synchronizing signal transmitted during each revolution of the transmitter drum 3 for controlling the synchronizing mechanism at the receiver to be hereinafter described. I prefer to transmit the tone or audio carrier signal of intensity greater than the maximum picture signal intensity for the cyclic synchronizing signals. In Figure l I schematically illustrate a preferred method for producing the synchronizing signals. The potentiometer 25 is adjusted for a suitable tone voltage to be intermittently impressed upon the control grid 2'! through coupling condenser 34.

The synchronizing signals are transmitted during a small predetermined portion of the time required for each revolution of the drum 3. A cam 35 attached to the drum shaft 6 actuates the contact blade 36 of a cam switch. Projection 31 of the cam 35 closes the cam switch circuit blades 3638 which are connected in series with the leads 39 and 40 from the potentiometer 25 to the coupling condenser 34. The angular position of cam projection 31 corresponds to the dead or underlap portion of the picture drum 3 where the dead edges of the picture being transmitted are fastened by clamping members 4|.

A carrier voltage preferably of increased intensity as compared to the maximum telepicture signals is accordingly transmitted cyclically during the transmission of a picture for synchronizing the receiving 'drum or drums for the picture. The cam switch l36l38 connects the second amplification stage E28 to a synchronizing signal of sufficient magnitude so that the signal strength of the synchronizing signal output of stage I28 is equal to or preferably greater than the magnitude of a white or normally maximum picture signal at the output. Adjustment of potentiometer 525 is accordingly made. It is to be understood that the cam switch Bit-438 is operated during the underlap or no picture portion of the telepicture cycle corresponding to about 10 or 15 degrees of the drum.

In adjusting the transmitter, potentiometer 9 .is suitably set for operating the photoelectric 75 cell 5. The potentiometer i6 is adjusted so that aoeaoei the bias for the control grid it permits a small tone signal to be transmitted during the black elements of the picture. The frequency of the carrier may. for example, be 2,000 cycles. In one embodiment. milliammeter til indicated .1 of a milliampere as the average direct current in the anode 22 circuit corresponding to black. A white picture element corresponds to the maximum value of transmitted carrier picture signal. The corresponding reading of the milliammeter til was 0.8 milhamper indicating an increased anode current.

Adjustments of the potentiometers it and 26 are made with black and white light signals impressed upon the photoelectric cell 5, giving corresponding meter 3t indications, in thisjexample,

Intermediate shading.

of .1 to .8 milliampere. between black and white corresponds to transmitted tone or carrier signals of intermediate intensity, and the meter 8% will have corresponding intermediate indications. The adjustments are made so that the maximum transmitted signal corresponding to white picture elements should not exceed a predetermined value. In half tone reproduction it is not desirable to have the maximum received signal, corresponding to white, too large, since the shading effect of the received picture will not be fully reproduced. It is preferable to have the maximum picture signal correspond to a light gray on the film at the receiver to insure all the variations between the maximum white signal and minimum black signal being reproduced.

A relatively small carrier output corresponding to black picture elements is preferably produced,

to have the picture signals override any background or line noise or interference signals, although a zero carrier output may be used for black. Although in my preferred telepicture system, the shading of a picture yields varying picture signal intensities, it is to be understood that black and white facsimile reproductions may be transmitted by such apparatus, the signals being represented by corresponding minimum and maximum carrier signal strengths.

It is to be understood that my preferred synchronizing system is applicable to other telepicture systems and circuits. For example, in a system dispensing with a tone or audio carrier corresponding to generator 50, a suitable impulse may be cyclically impressed upon an intermediate amplifier stage, preferably of signal wave shape which a white picture signal has. For example, if no chopper or audio-carrier for the picture signals is employed a suitable direct current biasing voltage cyclically applied to an intermediate stage of the signal amplifier would be used. I

The cyclic or synchronizing signals are transmitted during the underlap period or no picture period of each cycle so as not to interfere with the picture record or signals. In Figure 2, I illustrate a. schematic representation of a preferred telepicture receiving system controlled by the synchronizing signals for maintaining phase synchronism of the receiver record sheet with the transmitted picture. In this modification the tone carrier is not rectified-but is directly reproduced on the record sheet to obtain a broken or half-tone picture representation. As will be evident to those skilled in the art, rectification of the tone or audio carrier wave will produce picture signals corresponding in wave form to those at the photoelectric cell 5. However my nection device it is to be understood that is mereequally applicable to different telepicture or facsimile systems and Figure 2 will particularly set forth my invention at the receiver station.

Referring to Figure 2, the input II-I2 of audio amplifier I is either connected by wire lines to the output 6I-62 of the transmitter or to a suitable radio receiver (not shown) if a radio transmitter is used. If rectification of the picture audio carrier is desired the detector or demodulator is included within the amplifier unit 80.

The output of amplifier 80 is connected by leads 81-82 to the input stage of a push-pull class B amplifier I00, through the interstage transformer IOI. The/push-pull stage I00 comprises two amplifier tubes I02 and I03 connected in a well known manner. The output of the push-pull stage I00 is connected to the primary I04 of the output transformer I05. The output of the secondary I06 of transformer I is connected to a photolamp I01 containing a gas such as neon, for producing a light beam I0'Ia output in accordance with the telepicture signals received. The light output I0Ia from lamp I01 is suitably focused upon the receiving drum I08 by a lens system I09.

I prefer to use a neon crater photo-lamp I01 having a control electrode III) which is connected to one terminal I II of the transformer secondary I06 and an auxiliary or striking electrode III. The plate II2 of lamp I 01 is connected to the positive terminal of a suitable direct current source 3, the negative terminal of which is connected to ground. The other terminal II4 of the transformer secondary I06 is connected to the plate II2 through a variable resistance I I5 and fixed resistance I I6. The auxiliary or striking electrode III is connected to ground by lead II8. As is well known in the art, the auxiliary electrode II'I maintains a striking or discharge condition at the photo-lamp plate II2, so that it will always be in readiness to'respond to telepicture signals introduced between the plate H2 and the control grid III]. A by-pass condenser I I9 is connected between the output terminal I I4 and ground.

The receiver drum I08 is driven by a synchronous motor I20 connected to supply lines 8'. The lines 8 are preferably from the same alternating current supply as those of the transmitter 8 although such condition is not essential. The synchronous motor I20 drives drum I08 through the schematically indicated overrunning or positive clutch I2I. The details of the drive mechanism of my present invention are optional except that they are intermittently controllable by the synchronizing signals to maintain drum I 08 in phase synchronism. In my Reissue Patent'No. 19,575 I disclose a synchronously operated mechanism for connecting and disconnecting'a mechanical positive driving connection between the motor and the drum dependent upon signal actuation of a pawl engaging a ratchet wheel. The limits of the phasing positions are within the width of one tooth of the ratchet wheel.

In the parent application referred to and in my copending application Serial No. 72,991, filed April 6, 1936, is disclosed a preferred positive driving connection and disconnection means using an overrunning clutch corresponding to clutch I2I having a stop plate corresponding to stop plate I2Ia for operating the clutch. Although I prefer .to illustrate my present invention with a positive drive connection and disconly by way of example and not limitation.

Drum I08 is preferably driven at a slightly faster speed than the corresponding transmitter drum 3, for example, in a ratio of 101:100. The clutch I2I is under control of armature I22 which is actuated by the synchronizing magnet I23, to

maintain the drum I06 in phase synchronism with the transmitter drum 3 as will be hereinafter set forth. A direct current potential source I24 supplies the magnet I23 through the relay contacts I25-I26.

- The anode potential source I21 for the pushpull amplifier stage I00 is supplied to the center tap I20 of the primary I04 through the synchronizing cam switch I30I3I. A cam I32 is connected to the shaft I33 at the driven side of the overrunning clutch I 2I. The projection I34 of the cam I32 is the same angular position of shaft I33 as the film clamping members I35 of the I08 corresponding to the underlap or dead portion of. the drum. The cam switch I30I3I is normally maintained closed during the major portion of the rotation of cam I32, and the anode current from source I21 normally directly fiows to the push-pull amplifier stage I00 during the reception of the telepicture signals.

The cam switch I30-I3I is opened by the projection I34 of the cam I32 during the synchronizing or underlap period of the receiver. The underlap period of the drum I08 corresponds to the position of the film clamps I35 which clamp the dead edges of the record sheet. The projection I34 of cam I32 is angularly positioned to correspond to the position of the clamps I35. The anode current from source I2! is accordingly directed to the amplifier I00 through the synchronizing relay I36, which relay I36 is otherwise short circuited by switch I30-I3I. The synchronizing signal, as hereinabove described, occurs during the underlap period of the picture transmitter, and is preferably of greater magnitude than the telepicture signals. Synchronizing relay I36 is preferably a marginal relay responding only to the increased magnitude signals so as to avoid the possibility of interference of the synchronizing action by any of the telepicture signals. The push-pull amplifier I00 rectifies the alternating current synchronizing impulse in the anode lead, and the actuation of the relay I36 is by rectified or unidirectional current as will be understood by those skilled in the art.

Although I prefer to use synchronizing signals of increased intensity, and a marginal synchronizing relay, I have also successfully employed synchronizing signals of intensity equal to the "white picture element signals operating an ordinary relay. It is also to be understood that the synchronizing magnet I23 may be directly energized by the synchronizing signals, displacing the relay I36. However, in large receivers it is preferable to employ a relay since local energization of the magnet permits the design of a more powerful clutch control mechanism.

The receiver drum I08 is prepared for the synchronizing signal during the receiver drum I08 underlap by cam I32. The synchronizing signal will accordingly fiow through and energize the synchronizing relay I36 which then closes the relay contacts I25I26, locally energizing the synchronizing magnet I 23. The synchronizing magnet I23, when energized, will attract the clutch trip armature I22 away from stop plate I2Ia to permit the overrunning clutch I 2I to ms; 1. e., should the drum normally continue to drive the receiver drum Hi8 be in synchronism and in proper phase, the release of armature E22 away from the plate lZia would permit continued rotation without angular.

alteration. However, in the illustrated embodiment of my invention, the receiver drum is rotated slightly faster than the transmitter drum and the overrun'ning clutch 928 is accordingly momentarily tripped due to action of the armature E22 normally mechanically biased by spring i22a to tripping position; The synchronizing relay 9% actuates the synchronizing mag= net 923 to cyclically attract the armature i2? push-pull amplifier anode supply connection lead so that audio-carrier frequencies are self-rectified. Although I illustrate a synchronizing relay Ltd for operating a locally energized synchronizing magnet 523 it will be evident that the synchronizing magnet may be directly energized. The receiver cam switch mil-43! short circuits relay ltit during the picture translation period to avoid connection of any energy consuming device other than those normally connected in the telepicture receiver circuit and accordingly minimize frequency distortion. Upon reception of the synchronizing signal the drum N18 is adjusted to phase synchronism in its rotation cycle.

I claim:

1. In a telepicture system, a source of carrier current; means for transmitting said carrier with amplitude varying in accordance with the shading of a picture to be transmitted; means for cyclically transmitting said carrier with a predetermined amplitude; means for receiving and amplifying thev transmitted signals comprising a first and second amplifier tube connected in opposed relationship including a common anode potential lead said amplifier tubes being suitably biased to produce a change in the amplitude of the anode current of said lead in response to said cyclically transmitted signals; a receiver scanning mechanism comprising a rotatable member; means for synchronizing the rotation of said member comprising a synchronizing magnetconnected in series with said common anode po tential lead; means for normally short circuiting said magnet during the intervals of picture recording; and means for cyclically rendering said magnet responsive to said anode current for maintaining said member in synchronous rotation.

2. In a telepicture system, a source of carrier current; means for transmitting said carrier with amplitude varying in accordance with the shading of a picture to be transmitted in predetermined intervals corresponding to successive lines of said picture; means for cyclically transmitting said carrier with a predetermined amplitude greater than the maximum picture signal amplitude; means for receiving and amplifying the transmitted signals comprising a first and second amplifier tube connected in opposed relationship including a common anode potential lead said amplifier tubes being suitably biased to produce a change in. the ampiitude of the anode current ofsaid lead in response to said cyclically transmitted signals; a receiver scanning mechanism comprising a rotatable member; means for synchronizing the rotation of said member comprising a. synchronizing magnet connected in series with said common anode potential lead; means for normally short-circuiting said magnet during the intervals of picture recording; and

' means for cyclically rendering said magnet refirst and second amplifier tube having a common anode potential lead said amplifying means being adjusted to produce a self-rectifying action of the signals in said lead; a scanning mechanism comprising a rotatable member; means for synchronizing the rotation of said member comprising a synchronizing magnet connectedin said common anode potential lead; means cooperable with said rotatable member for normally short circuiting said magnet during the intervals of picture recording comprising a cam switch connected across said magnet, and for cyclically rendering said magnet responsive to said anode current for maintaining said member in synchronous rotation.

4. In a. telepicture system, a source of carrier current; means for transmitting said carrier with amplitude varying in accordance with the sheding of a picture to be transmitted in predetermined intervals corresponding to successive lines of said picture; means for transmitting said carrier with a predetermined amplitude greater than the maximum picture signal amplitude between the picture signal intervals; means for receiv ing and amplifying the transmitted signals comprising a first and second amplifier tube connected in class B push-pull relationship including a common anode potential lead; a scanning mechanism comprising a rotatable member; means for synchronizing the rotation of said member comprising a direc't'current synchronim ing magnet connected inseries with said common anode potential lead; means for normally short circuiting said magnet during the intervals of picture recording; and means for cyclically rendering said magnet responsive to said predetermined amplitude signals for maintaining said member in synchronous rotation.

5. In a telepicture system, a source of carrier current; means for transmitting said carrier with amplitude varying in accordance with the shading of a picture to be transmitted in predetermined intervals corresponding to successive lines of said picture; means for transmitting said carrier with a predetermined amplitude greater comprising a first and second amplifier tube ineluding a common anode potential lead said amplifying means being adjusted to produce a selfrectifying action of the signals in said lead; a

scanning mechanism comprising a rotatable drum; means for synchronizing the rotation of said member comprising a direct current synchronizing magnet connected in series with said common anode potential lead; means for normally short circuiting said magnet during the intervals of picture recording comprising a cam switch connected across said magnet; and means for cyclically rendering said magnet responsive to said anode current for maintaining said drum in synchronous rotation comprising a cam connected to said drum for opening said cam switch between successive lines oi picture recording.

6. In a telepicture system, a source of carrier current; means for transmitting said carrier with amplitude varying in accordance with the shad- 4 ing of a picture to be transmitted in predetermined intervals corresponding to successive lines of said picture; means for cyclically transmitting said carrier with a predetermined amplitude;

means for receiving and amplifying the transmitted signals'comprising a first and second ampiifier tube connected in class B push-pull relationship including a common anode potential lead; a scanning mechanism comprising a rotatable member; means for synchronizing the rotation oi said member comprising a synchronizing relay connected in series with said common anode potential lead; means for normally short circuiting said relay during the intervals 01. picture recording comprising a cam switch connected across said relay; and means for cyclically rendering said relay responsive to said predetermined amplitude signais for maintaining said member in synchronous rotation to actuate said magnet comprising a cam connected to said member for opening said cam switch between successive lines of picture recording.

G. H. FINCH. 

